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Congrats Dave! any chance of a sound file?
http://help.soundcloud.com/customer/portal/articles/626942

I suspect that when you put the car on a Dyno that you will go up to around 130-132 mains. I'm running a similar cam but have 39mm Keihins with 155 mains which in Mikuni is around the 130-132, I have yet to run mine on a Dyno either but was able to pick up a few more RPMs by going from 152 to 155s. I did Dyno the A12 and when we got close the last change was going up one jet size, which was good for 4 HP, something I may not have done because the car pulled really well even though it was a touch lean.

As for the throttle cable I had a custom one made, this is fairly common for motorcycles, my buddy had enough of the parts in his shop to make one up.

I have very little experience with DCOEs but the sports racer guys who used A-Series engines picked up 10 HP by simply switching to FCR carbs.

Tom

That's a massive increase at 10hp, I'm beginning to miss bike carbs......

Hey zigy, at an estimate what did it cost u for the carby set up?
Cheers Corey

Interesting statement considering those Carbs have just like Webers, Dellorto's and Solexes Main jets, Idle Jets, Air Correctors, Needle Jets (Emulsion Tubes) and the Air Corrector's are High speed and low speed (Weber low speed air correction is built into the idle jet with differing F numbers designating the air correction hole size).

In fact they have as many Jets as the others and add a couple more options such as Needle tapers and lengths, Multiple tapers and as well Slide cutaways to add into the mix when tuning.

CV Vacuum Carbs also add into the mix different spring lengths and rates to boot, So they are not actually any simpler.

The Biggest difference is that besides picking a size with Webers etc such as 40mm, 45mm or the rarer 42mm, 48, or 50mm and 55mm base sizes you then can alter Main and Auxiliary Chokes or venturi's to fine tune to the engine characteristics.

With Bike carbs whilst good you must make sure you get the right size to suit from the beginning as there is no way of changing Choke sizes other than a new set of different carbies.

So in truth there are pro's and con's to both approaches and if you know what you are doing both types can be jetted to work, If you do not know then both can and will be problematical to make work right.

Therefore just because you lucked out with a set of bike carbs that worked OK with your particular setup does not mean everyone else will be as lucky unless they do some serious research before jumping in and that applies to all carbs, Car specific or Bike specific.

There are also many different non interchangeable Mikuni and Keihin jets to be aware of with different variations of carbs.

With the FCR Bike carbs there is also a very real problem that can cost you an engine they run what is called a Vacuum plate on the slide and the stock ones have a releif on both sides and they break off a couple of sections of these plates after a while, There are billet replacements relieved on one side only that are better but the vaacuum plate is a weakness in the design to be aware of and check on a regular basis.

Not so bad on a race car but a pain in the Posterior for a road driven vehicle to check for cracks on a regular basis, I see them break more often on single cylinders with stronger vacuum pulses but they do also break on four cylinder engines.

While I have heard of vacuum plate issues it seems to be, as you pointed out, most common on singles. I have not heard of anyone with multis having the issue. Also as pointed out there is a replacement. I run the FCR carbs mainly because I scored them cheap but they do offer an advantage in flow, here the USA the SCCA does not allow non-butterfly actuated carbs in production classes.......I'm told due to the increase flow and the fixed choke/Venturi size. Under the possible heading of urban myth slide carbs do seem to offer better response than butterfly carbs. Note CV carbs fall under butterfly carbs.
As for additional jetting options that is one of the other features I like about the FCR carbs; I changed the needles to ones with a different taper and L1 measurement to get mine exactly dialed in. Once the car was dialed in it has been just a matter of minor jetting changes. Now there is one downside to FCR.......the little clips on the tops of the needle for adjusting the height, they are quite easy to loose. I use needle nose vice grips and keep extra clips in my jet box.

Tom

Maybe 2 more things need to be considered - Manifold design and weber/bike carbs inner flow paths.

Bike carbs on an evenly spaced 4 cylinder require manifolds with less turns or changes for fuel mix
to hit the sides and bike carbs dont use chokes to create turbulence which differs from slides.
Yet even on an A series, slightly offset inlets due to 2/3 exhausts ports doesnt create an issue
but on longer L series engines it could be more of an issue compared to webers.

In the above 2 points on an A series, bike carbs seem to good/better paths to inlet ports provided
they are well matched and better go smaller than too large in most cases.

Dave still waiting for a sound file :)

Tom I am not so sure about "Better Response" compared to CV carbs I do think because CV carbs feel smoother like Fuel Injection does they may not feel as Punchy.
It is amazing when properly tuning CV carbs and getting the low and high speed air correction right just how much power they can make, Often more than FCR carbs.

On a side note but also relevant, With Nissan Datsun HItachi SU type carbs Fuel level is vital to correct mixture, Too high and they go really rich and of course the opposite also applies, just a 1mm change can see Air Fuel Mixtures go from 12>1 to 15>1 at low to mid speed ranges.

FCR carbs unless you run something like Factory Pro modified Needle Jets really are a MotoCross On-Off sort of carb fueling wise, Fine for the race track maybe not so nice on the road in downtown Las Vegas Traffic.
The Issue with FCR carbs is in fact poor emulsion performance especially if you need to go below a 180 Main Air Corrector Jet, Then Mixture quality is rubbish and even if the Dyno readout says the Mixture is OK the power drops off, For that reason they really need Big Air correctors for the main circuit or better Emulsion Tubes (Needle Jets) with some bloody air bleed holes as FCR's don't have any at all stock.

Carburetors are not quite as simple as some people think.

Steve, I previously ran the GX carbs on my car and people offered up all sorts of "hot tips" for setting them up. I tried one or two, mostly to do with oil in the dash pots and went back to the factory settings. Absolutely nothing wrong with them, they would still be on the car if it weren't for the deal I got on the FCR carbs.
We also used the standard CV carbs on our Yamaha powered sports racer and the only issue was one of fuel slosh/starvation due to high G loads
Now I will have to disagree with the FCR carb; it is the standard carb on my Beta 520 and you can lug the bike or if you're stupid whack the throttle open like a gorilla. All the magazine tests also raved about how well the carbs worked. Same goes for the 1200 it will motor around the pits without protest and pull from as low as 2500 rpms with a 278 degree cam. When I was running the GX cam in the motor with the FCR carbs it would have been perfectly streetable. The only issue I ever had with drivability was due to 286 degree cam which had a lot of overlap; it was unhappy below 4500 rpms, it was even a pain to put on the trailer. There are a couple of idiosyncratic things with the FCRs as you mentioned but I simply jetted accordingly.
One thing I will totally agree with is that carbs are not as simple as people think. I am also amazed at what people will tolerate on all types of carbs. My Ford F350 struggled to get though smog, the needles started raising up fully at fairly low rpms causing it to run rich. Simply changing the springs cured the smog issue and the gas mileage went from 10mpg to 12mpg.

Tom